Heart disorders are a common cause of death in developed countries. The major cause of heart disease in developed countries is impaired blood supply. The coronary arteries, which supply blood to the heart, become narrowed due to atherosclerosis and part of the heart muscle is deprived of oxygen and other nutrients. The resulting ischemia or blockage can lead to angina pectoris, a pain in the chest, arms or jaw due to a lack of oxygen to the heart, or infarction, death of an area of the myocardium caused by ischemia.
Techniques to supplement the flow of oxygenated blood directly from the left ventricle into the myocardial tissue have included needle acupuncture to create transmural channels (see below) and implantation of T-shaped tubes into the myocardium. Efforts to graft the omentum, parietal pericardium, or mediastinal fat to the surface of the heart had limited success. Others attempted to restore arterial flow by implanting the left internal mammary artery into the myocardium.
Modernly, coronary artery blockage can be treated in a number of ways. Drug therapy, including nitrates, beta-blockers, and peripheral vasodilatator drugs (to dilate the arteries) or thrombolytic drugs (to dissolve clots) can be very effective. Transluminal angioplasty is often indicated--the narrowed diameter of the opening or lumen of the artery, clogged with atherosclerotic plaque or other deposits, can be increased by passing a balloon to the site and inflating it. In the event drug therapy is ineffective or angioplasty is too risky, the procedure known as coronary artery bypass grafting (CABG) may be indicated. The procedure requires the surgeon to make an incision down the center of the patient's chest and the heart is exposed by opening the pericardium. A length of vein is removed from another part of the body, typically the leg. The section of vein is first sewn to the aorta and then sewn onto a coronary artery at a place such that oxygenated blood can flow directly into the heart. CABG is a major surgical procedure which requires the installation of the heart-lung machine and the sternum must be sawed through.
Another method of improving myocardial blood supply is called transmyocardial revascularization (TMR), the creation of channels from the epicardial to the endocardial portions of the heart. The procedure using needles in a form of "myocardial acupuncture" has been used clinically since the 1960s. Deckelbaum, L. I., Cardiovascular Applications of Laser Technology, Lasers in Surgery and Medicine 15:315-341 (1994). The technique was said to relieve ischemia by allowing blood to pass from the ventricle through the channels either directly into other vessels perforated by the channels or into myocardial sinusoids which connect to the myocardial microcirculation. The procedure has been likened to transforming the human heart into one resembling that of a reptile.
In the reptilian heart, perfusion occurs via communicating channels between the left ventricle and the coronary arteries. Frazier, O. H., Myocardial Revascularization with Laser--Preliminary Findings, Circulation, 1995; 92 [suppl II]:II-58-II-65. There is evidence of these communicating channels in the developing human embryo. In the human heart, myocardial microanatomy involves the presence of myocardial sinusoids. These sinusoidal communications vary in size and structure, but represent a network of direct arterial-luminal, arterial--arterial, arterial-venous, and venous-luminal connections. This vascular mesh forms an important source of myocardial blood supply in reptiles but its role in humans is poorly understood.
Numerous studies have been performed on TMR using lasers to bore channels in the myocardium. Histological evidence of probable new vessel formation adjacent to collagen occluded transmyocardial channels exists. In the case of myocardial acupuncture or boring, which mechanically displaces or removes tissue, acute thrombosis followed by organization and fibrosis of clots is the principal mechanism of channel closure. By contrast, histological evidence of patent, endothelium-lined tracts within the laser-created channels supports the assumption that the lumen of the laser channels is or can become hemocompatible and that it resists occlusion caused by thrombo-activation and/or fibrosis. A thin zone of charring occurs on the periphery of the laser-created transmyocardial channels through the well-known thermal effects of optical radiation on cardiovascular tissue.
U.S. Pat. No. 4,658,817 issued Apr. 21, 1987 to Hardy teaches a method and apparatus for TMR using a laser. A surgical CO.sub.2 laser includes a handpiece for directing a laser beam to a desired location. Mounted on the forward end of the handpiece is a hollow needle to be used in surgical applications where the needle perforates a portion of tissue to provide the laser beam direct access to distal tissue.
U.S. Pat. No. 5,125,926 issued Jun. 30, 1992 to Rudko et al. teaches a heart-synchronized pulsed laser system for TMR. The device and method comprises a device for sensing the contraction and expansion of a beating heart. As the heart beat is monitored, the device triggers a pulse of laser energy to be delivered to the heart during a predetermined portion of the heartbeat cycle. This heart-synchronized pulsed laser system is important where the energy and pulse rate of the particular type of laser are potentially damaging to the beating heart.
U.S. Pat. No. 5,380,316 issued Jan. 10, 1995 and U.S. Pat. No. 5,389,096 issued Feb. 14, 1995 both to Aita et al. teach, respectively, systems and methods for intra-operative and percutaneous myocardial revascularization. The '316 patent is related to TMR performed by inserting a portion of an elongated flexible lasing apparatus into the chest cavity of a patient and lasing channels directly through the outer surface of the epicardium into the myocardium tissue. In the '096 patent TMR is performed by guiding an elongated flexible lasing apparatus into a patient's vasculature such that the firing end of the apparatus is adjacent the endocardium. Channels are created directly through the endocardium into the myocardium tissue without perforating the pericardium layer.
TMR is most often used to treat the lower left chamber of the heart. The lower chambers or ventricles are fed by the more distal branches of the coronary arteries. Distal coronary arteries are more prone to blockage and resulting heart muscle damage.
To date, TMR channels have been created surgically straight through the epicardial surface into the myocardium, or in the alternative, vascularly via catheter from the endocardium within a chamber straight radially outwards into myocardium. In either case, an essentially single-ended channel is ultimately formed.
A need exists in the prior art for maintaining patency of TMR channels, for increasing blood flow in channels that are closed at the epicardium, or created percutaneously, for reducing trauma to the epicardial layer of the heart, and for creating multiple channels through a single opening, particularly in areas where access and visibility are limited.
Thus, broadly, it is an object of the present invention to provide an improved method and device for laser-assisted transmyocardial revascularization (TMR).
It is a further object of the present invention to provide a method for performing TMR in which branched channels are created in the myocardium through a single access opening thereby reducing trauma to the exterior of the heart.
It is a further object of the present invention to provide a method for performing TMR in which branched channels are created in the myocardium to allow flow of blood and other factors through channel branches from myocardial capillaries.
It is a further object of the present invention to provide a device for performing TMR in which branched channels are created in the myocardium.
It is a further object of the present invention to provide a device for performing TMR, particularly suitable for use in areas where access and visibility are limited, in which branched channels are created in the myocardium, through a single opening, by providing a fiber advancing mechanism and a laser delivery means having needle orientation means.
It is a further object of the present invention to provide a device for performing TMR in which branched channels are created in the myocardium by providing a hand-held device with a fiber advancing mechanism and a laser delivery means with needle orientation means.
It is a further object of the present invention to provide a device for performing TMR in which branched channels are created in the myocardium by providing a finger-tip operated device with fiber advancing mechanism and a laser delivery means with needle orientation means.